Demountable magnetron with metal-to-metal



Jan. 31, 1956 A. A. PHILLIPS ET AL 2,733,380 DEMOUNTABLE MAGNETRON WITH METAL-TO-METAL VACUUM TIGHT JOINT Filed June 9, 1952 /N VENTORS ALEXANDER A. PHILLIPS W/LL/AM A.SMITH, J/a

BY idi;

the parts without damaging the tube due to the DEMOUNTABLE MAGNETRON WITH METAL- TO-METAL VACUUM TIGHT JOINT Application June 9, 1952, Serial No. 292,562 4 Claims. (Cl. 315-3953) This invention relates to vacuum-tight metal-to-metal seals.

In sealing certain metal enclosures vacuum tight, it is not desirable to apply the amount of heat necessary with such processes as brazing. The application of heat, for instance, to the resonant cavity of a magnetron type of election discharge tube may well adversely affect the parts within the cavity. One of these adverse efiects is oxidization of both the outside of the cavity and the interior. if a cavity of this type is sealed by brazing, it is very difiicult to reopen the cavity to inspect or replace any of necessity for applying intense heat.

By the use of the seal of the present invention, these ditficulties are avoided. The seal is formed by two overlapping edges of metal bound tightly together by a continuous band of metal shrunk onto the outside of the overlapping edges. The band of metal is formed so that it expands sutficiently when heated to red heat to just slip on over the parts to be joined. The heated band is slipped over the pieces forming the joint while they are held in position. As the band cools it contracts, tightening the joint until it is vacuum tight. Should it be desired to inspect the interior of the evacuated cavity, or to replace an internal part, such as the cathode assembly, all that is necessary is to cut through the band and separate the parts. Thus the disassembly operation avoids the use of intense heat with its attendant risk of damaging the parts. The cavity can be resealed' by shrinking a new heated band onto the joint.

The foregoing and other advantages, objects and features of the invention will be better understood from the following description taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a section along the line 11 of Fig. 2 showing a cavity magnetron made with the seal of the invention; and

Fig. 2 is a section taken along the line 2-2 of Fig. 1.

In the drawings, the reference numeral designates generally the resonant cavity of a magnetron. The magnetron comprises an anode having a plurality of vanes 12 forming resonant cavities. A cathode 13 is located with its axis at the center of the anode vanes 12. The cavity 10 is formed with a cylindrical outer wall 14 and a circular top plate 15. A pole piece 16 is inserted coaxially with the cathode 13 through an opening in the plate of the cavity 10. The upper end of the cathode 13 extends into a hole 17 in the pole piece 16. Strapping 18 of one of the Well-known types is provided across the inner ends of the vanes 12. The output is obtained from one of the resonant cavities between the vanes 12 by the coaxial probe 20 comprising a central conductor 21 terminating in a loop, and an outer conductor 22 terminating in a bushing 23 that fits into the side wall 14 of the magnetron. The bottom of the magnetron cavity 10 is formed of a cup-shaped cap 24 that fits over the lower end of the cylindrical walls 14 of the resonant cavity 10. A second pole piece 25 is inserted in an opennited States Patent ing formed at the center of the cap 24. This pole piece 25 is formed with a hole 25a concentric with the axis of the cathode 13 to receive the lower end of the coaxial connector 26 of the cathode 13. This coaxial connector 26 has a central connector 27. The upper end of the cathode 13 is terminated in a coaxial connector 26a. This cathode construction and mounting is best shown in the application of William C. Brown for United States Patent No. 583,624, filed March 19, 1945, and which is now U. S. Patent No. 2,624,861, granted January 6, 1953.

The cap 24 is formed with an upwardly projecting wall 28 made to fit into recess 30 formed in the end of the cylindrical wall 14 of the magnetron cavity 10. A thinner portion 31 of the wall 28 of the cap 24 projects beyond the recess 30. The cap 24 is made of a highly conductive material such as copper, as is the wall 14, and the end plate 15. A ring 32 is formed of a metal having a somewhat greater coeflicient of expansion than the copper of the cap 24. Stainless steel has been successfully used for this purpose. The ring or band 32 is formed with a double taper 33 so that it makes contact with the thin extension 31 of the cap 24 over a restricted area. This ring 32 is made with an inside diameter at the region of contact less than the outside diameter of the cap 24 Walls 14 that the resulting at normal temperatures. The ring is heated to a point where it expands sufliciently to increase its inside diameter at the region of contact to an amount greater than that of the outside diameter of the cap 24. In the case of the stainless steel ring mentioned above, this temperature was found to be red heat or approximately 1400 F. (760 C.). When the ring 32 has expanded sufliciently, it is slipped over the cap 24 and permitted to cool in place. The resulting constrictive pressure forces the edge 31 of the cap 24 so tightly against the joint is vacuum tight. As the tube is heated in use, the copper will expand together with the ring and the seal will not loosen. The relative masses and thermal conductivity of the magnetron cavity 10, the cap 24, and the ring 32 are such that, while the ring itself is at a high temperature when it is applied, it does not increase the temperature of the magnetron cavity substantially. In a representative case, the application of such a ring of stainless steel heated to 760 C. to a cavity of copper only heated the cavity to a temperature of C. Thus, there is no danger of the heat transmitted from the ring 32, in the forming process, damaging the parts of the cavity or parts within the cavity, as is likely to be the case in brazing and soldering Where the parts to be joined must themselves be brought to a high temperature in order to assure a vacuum-tight seal.

When it is desired to break the seal, there is no need to apply heat as would be necessary if the joint had been brazed or soldered. The ring 32 is simply cut through and pried off. The magnetron can then be disassembled, the parts inspected, repaired or replaced, as desired, and the sealing process repeated with another ring. The particular type of cathode structure shown is one that permits the magnetron to be readily disassembled when such a seal is used. It can be readily seen that with this type of mounting, a cathode subassembly comprising the cathode 13, the cathode connectors 26 and 26a, the pole piece 25, and the cap 24 could easily be removed and replaced by a new one, thus readily salvaging the anode structure of magnetrons having defective cathodes.

The seal of this invention can be used for forming vacuum-tight metal-to-metal seals wherever they are needed. While the seal is shown as applied to the joining of two cylindrical pieces, it can also be used to join pieces of other shapes. The ring or band 32 is shown formed with a triangular cross-section in the region of contact. Other configurations of the band 32, such as curved surfaces, can be used that. provide a restricted area of contact. While it is desirable to reduce the area of contact to a minimum, this is not essential to the success of this type of seal.

This completes the description of the particular embodiments of the device disclosed herein. However, many modifications thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. Accordingly, it is desired that this invention be not limited by the particular details of the embodiments described herein except as defined by the appended claims.

What is claimed is:

1. An electron discharge device of the magnetron type comprising an anode member formed with an evacuated resonant cavity comprising. two parts of oxidizable metal with overlapping edges held together in a vacuumtight joint by a restricting metallic band having a reduced area in. the region of said joint.

2. An electron discharge device of the magnetron type comprising an anode member formed with an evacuated resonant cavity comprising two parts of oxidizable metal with overlapping edges at a' region of reduced wall thickness held together in a vacuum-tight joint by a restrict- 4 ing metallic band having a reduced area in the region of the said joint.

3. An electron discharge device of the magnetron type comprising an anode member formed with an evacuated resonant cavity comprising two cylindrical parts of oXidiZable metal with overlapping edges held together in a vacuum-tight joint by a restricting metallic ring having a reduced area: inthe-region of the said joint.

4. An electron. discharge device of the magnetron type comprising an anode member formed with an evacuated resonant cavity comprising two cylindrical parts of oxdizable metal with overlapping edges at a" region of reduced' wall thickness held together in a vacuum-tight joint by a restricting metallic ring having a reduced area in the region of the said joint.

References Cited in the file of this patent UNITED STATES PATENTS 351,263 Hemphill Oct. 19,. 1886 373,093 Rew Nov. 15, 1887 418,752 Rogers Jan. 7, 1890 1,687,343 Madden Oct. 9, 1928 1,748,138 McBride -n. Feb; 25, 1930 2,546,976 Clark et al'. Apr. 3, 1951 

